The internal combustion engine has now been with us for many decades and has become a most familiar design wherein the reciprocating piston uses connecting rods to connect the piston to the crank pins of the crank shaft to translate linear reciprocating motion of the pistons to rotary motion of the crank shaft.
For the most part, a connecting rod is articulable at both ends where it attaches to the piston and crank pin. This piston is connected to the connecting rod by a wrist pin that passes through the piston and the connecting rod. For the most part, these kinds of designs for such internal combustion engines are known as slider crank engines. Nonetheless, time has proven that these types of internal combustion engines do have significant disadvantages and limitations.
There has been a push, particularly now that fossil fuels are becoming scarce and there is a greater community emphasis to protect the environment by way of exhaust coming from conventional internal combustion energy, to improve upon the conventional slider crank engine.
The Scotch yoke has been used in certain engine designs seeking to utilize cyclic dynamics over the slider crank engines. For the most part, traditional Scotch yoke engines connect two horizontally opposed pistons by non-articulable connecting rods to a shuttle having a slot which accommodates the crank pin of a crank shaft. Guide services constrain the motion of the shuttle to a linear path and the crank pin slides within the slot as the crank shaft rotates through its range, converting the linear reciprocating piston movement to rotary crank shaft motion.
As the person skilled in the art will realise, the slot within the shuttle must be at least as wide as the crank pin diameter and at least as long as the diameter of the crank pin travel. Further, as the piston rod is part of a piston plate or the like which is restricted to linear reciprocated motion, any movement of the crank shaft will automatically see the piston extended or retracted away from any settable momentary position, including the sparking position.
A present trend in engine design is to increase engine rpm using the conventional piston rod with a Scotch yoke structure. The use of convention scotch yokes is not always possible for the most part as the piston stroke is short and the time available for drawing air into the combustion chamber is very short. This causes combustion at less than the ideal 15 to 1 air/fuel ratio for the fuel which in turn, leaves unburnt fuel to be exhausted as pollutants into the atmosphere. With the exhausted unburnt fuel goes wasted energy which should have been converted to power to drive the piston.
What effectively is happening in both currently available slider crank engines as well as Scotch yoke based designs is that there is inefficient coupling between the piston rod and the crank shaft. In con-rod engines, a greater torque can be achieved at specific crank angles by increasing the length of the stroke, that is, the height of the connecting rod and thus the height of the engine. This however is not practical in many applications and there are various associated disadvantages.
The skilled addressee would realise that a Scotch yoke transmits its force to a centre line location of a crank pin (a conventional crank) at a 90° crank angle for its maximum torque. Therefore, the linear travel of a Scotch yoke is always consistent, whether or not it has been modified for dwell, and its maximum leverage is always at 90°. The crank shaft typically has a sliding/rolling element associated therewith that slides/rolls on the yoke for the entire 360 degree rotation of the crank shaft. Scotch yokes therefore have very limited application.
The present inventor has recognised the need for an improved means of translating linear to rotary motion, and vice versa, and in combustion engine applications an improved relationship between yoke and crank, and yoke and piston, ensuring that torque is maximised at a much greater force than for example a scotch yoke.
International Patent Application No. PCT/AU2011/000398, owned by the present Applicant and incorporated by reference herein, provides an example of a cam yoke type engagement which overcomes some of the aforementioned problems by providing a mode of operation that is interchangeable between a crank mode and a cam mode in one revolution of the crank shaft to achieve increased leverage (pressure transferred to a greater leverage point) and a piston dwell time for improved combustion. That invention involved the use of a bearing or wheel member rotatable about an end of a crank arm associated with the crank shaft, and engageable with an inner surface of a linearly moveable yoke structure with which a piston is associated. The inner surface includes a shoulder portion which serves to momentarily interrupt the transformation of linear motion of the piston into rotary motion of the crank, the bearing thus undergoing a function change from a crank mode to a cam mode.
The Applicant's prior international application thus proposes an assembly which improves combustion and introduces a leverage effect to increase maximum torque at a much greater force than a conventional scotch yoke. However, while the Applicant's own prior art serves its purpose and provides a unique advantage over conventional assemblies of this type, the present invention seeks to provide a further improved assembly by addressing issues such as, but limited to the following:                leverage not being fully maximised;        combustion and energy efficiency not being optimum;        component design and configuration being such that the assembly involves a large number of parts and does not lend itself to simplified manufacturing;        component design and configuration being such that the assembly is not easily adjustable for leverage/dwell to suit different applications; and        vibration/rattle issues resulting from the use of multiple components and by significant load bearing against a single rolling element.        
It is therefore an object of the present invention to overcome at least some of the aforementioned problems or to provide the public with a useful alternative.
It is to be understood at the outset that any reference to a “cam effect” herein should not to be interpreted as being the same phenomenon as the earlier mentioned “cam mode” of the bearing in the Applicant's prior art patent application.
Further objects and advantages of this invention will become apparent from a complete reading of the following specification.